Cattle Heat Stress for Dairy Cows

Dairy Cattle Heat Stress

What is Cattle Heat Stress?

Cattle Heat Stress Costs Producers Money

Heat and humidity are tough on cattle. Rising temperatures and humidity result in increasing body temperatures, with very negative consequences. Even cattle living in fairly moderate climates may experience periods of heat stress. Heat stress causes a wide range of behavioral and medical issues in cattle – all of which cost the dairy or beef producer money.

"One of the most common mistakes when managing heat stress is not knowing when heat stress begins."

Evaluation of OmniGen-AF® in Lactating Heat‐stressed Holstein Cows
- University of Wisconsin Extension “Managing Heat Stress Podcast Series

  • Cattle Heat Stress leads to loss of appetite Loss of appetite

    Cattle lose their appetite when their body temperature exceeds critical thresholds, causing reduced dry matter intake, milk yield, growth and weight gain and resulting in the loss of feed rations to spoilage.
  • Cattle Heat Stress leads to reduced fertility Reduced fertililty

    Heat stress impacts fertility and reproductive efficiency, causing losses in cow calf and dairy operations.
  • Heat stressed cattle are prone to health issues Prone to health issues

    Medical problems can quickly arise in heat stress situations, including lameness from disruption of the digestive process, impaired immunity, and in the worst cases, rapid death.
  • Cattle heat stress leads to reduced milk production Reduced Milk Production

    Both milk yield and quality are reduced by heat stress. The level of mastitis and somatic cell counts rise as temperature and humidity levels increase.

Heat Stress Management

Reducing cattle heat stress, and the associated losses in productivity and performance, is worth every cattle manager’s attention. Effective heat stress management requires an understanding of all factors contributing to a cow’s heat energy balance.

Heat Stress and Cold Stress on LIvestock

Cattle generate heat metabolically through digestion and activity and also accumulate heat from their environment – ambient temperature, solar radiation and radiant heat from the ground (reflected solar radiation as well as heat generated by decomposing manure). They dissipate heat through non-evaporative cooling – radiation, conduction and convection back into their environment – as well as through evaporative cooling – sweating and panting. They can also reduce heat load through taking in cool water. In persistent hot, sunny, humid conditions, the cooling mechanisms are insufficient to dissipate all accumulated heat, and the cow’s body temperature begins to rise, triggering the cascade of negative heat stress impacts.

Heat stress management practices include providing shade, enhancing ventilation by adding fans or passive ventilation, enhancing evaporative cooling with sprinklers, providing cooled water, and modifying feed to increase dry matter intake and reduce waste. Each of these practices ALSO cost money, so the smart producer’s goal is to implement management practices every time they are needed, but ONLY when they are needed.

Fortunately, extensive academic and industry research into livestock heat stress management has generated excellent heat stress reduction guidance that is based on proven cattle-specific environmental measurements and models. Implementing a measurement-based heat stress management plan is the most effective way to minimize heat stress losses without wasting money.

"Production, reproduction, and animal health are all impaired by hyperthermia. The physiological and production responses to heat stress are well documented, but not fully understood. During HS, respiration rate and body temperature increase while feed intake, milk yield, and reproduction decrease."
Evaluation of OmniGen-AF® in Lactating Heat‐stressed Holstein Cows
- L. W. Hall*, F. A. Rivera*, F. Villar*, J. D. Chapman§, N. M. Long¶, and R. J. Collier*
*University of Arizona, §Prince Agri Products, ¶Clemson University

Objective and accurate measurements at pen level are critical to planning your heat management strategy.

How to measure cattle heat stress


By the time signs and symptoms of heat stress such as panting and drooling are visible in your cattle, production losses have already begun. Cattle suffer heat stress before people do, so simply waiting until you feel the heat intensify will also not ensure heat losses are prevented. Because cattle accumulate heat, if they do not have an opportunity to dissipate heat through overnight temperature cooling or environmental modifications, your herd's heat problems are increasing invisibly.

The first step in any cost-effective heat management plan is to accurately measure conditions wherever cattle are contained, at the pen level, and then determine your cattles’ risk of heat stress injury. To provide more accurate management guidance, researchers and government agencies have developed a variety of cattle-specific measurements and management models:

Heat Stressed Dairy Cow

"In dairy cows, higher temperatures lower milk output and reduce the percentages of fat, solids, lactose, and protein in milk."
- Kadzere et al., 2002; St-Pierre et al., 2003; West, 2003

Cattle Specific Heat Stress Measurements and Models

Kestrel meters can measure heat stress and heat load in cattle

THI - Temperature-Humidity Index

THI is calculated based on ambient temperature and relative humidity and has been extensively applied in research and management to represent the overall impact of moderate to hot conditions on cattle, especially those who are housed. Although THI is similar to the Heat Index typically reported in the local weather report, it is calculated differently. Accordingly, to obtain THI without a dedicated instrument, it is necessary to take a local temperature and humidity reading and refer to a reference table or perform calculations.

HLI – Heat Load Index

The limitation of THI is that is does not take into account sun, air flow, or accumulation effects. HLI is a more complete environmental index which includes temperature, relative humidity, and the additional parameters of solar radiation and wind speed. These added parameters are most important for assessing heat stress risk in exposed, unshaded cattle. These parameters are derived from the Globe Temperature – an advanced meteorological measurement which uses a heat-absorbing metal globe. Because Globe Temperature is not available on traditional weather stations, it has previously been difficult to implement management practices based on HLI.

AHLU – Accumulated Heat Load Units

AHLU is the most complete cattle heat stress model – addressing the fact that cattle accumulate heat load during prolonged heat events where they have insufficient environmental night cooling. THI and HLI alone may not predict the level of cattle heat stress because they do not address this accumulation impact.

How is Cattle Heat Risk Calculated

Calculating AHLU

In order to calculate AHLU, an HLI Threshold is determined for each group of cattle. This is the HLI value above which those cows will start to accumulate heat. The HLI Threshold will vary depending on many factors, including the breed, color, feed state, acclimatization and general health of that group of animals, as well as the environmental conditions of their housing:

(The Bos Taurus breeds prevalent in Western beef and dairy operations are particularly subject to ill effects from heat as they are less efficient at cooling themselves than Bos Indicus breeds.)

Because AHLU is an accumulation measure, it must be measured at the animals' location over an entire heat event to provide accurate management guidance. Previous methods of measuring and calculating AHLU were extremely time-consuming and complex, requiring the use of very expensive equipment to obtain the base measurements, referencing complex tables to obtain the correct HLI Threshold, then entry of hourly measurements into spread sheets to calculate the accumulated heat load units. All in all, a practice that is not likely to be adopted by most cattle or dairy operations, no matter how effective.

"In 2010, heat stress lowered the value of annual milk production for the average dairy by about $39,000, which equates to $1.2 billion in lost production for the entire dairy sector."
- Climate Change, Heat Stress, and U.S. Dairy Production – Nigel Key, Stacy Sneeringer, and David Marquardt

The Kestrel Solution

Kestrel has been building weather and environmental meters for over two decades. For many farmers, a pocket Kestrel meter has been their standby tool for monitoring conditions for spraying, irrigation, harvesting and processing. Kestrel also has developed some of the most advanced meters on the market for monitoring human heat stress in athletics and demanding work scenarios. Kestrel has brought its farming experience and technical and physiological expertise to bear to develop affordable, easy-to-use solutions to allow cattlemen and dairy operators to accurately measure and monitor cattle heat stress conditions without reference to complex tables and spreadsheets.

Kestrel’s line of Agriculture Meters includes handheld and portable solutions for heat stress measurement specific to dairy and beef cattle. The Kestrel 5000AG Livestock Environmental Meter captures and logs vital information on micro-climate conditions allowing you to make informed, data-backed decisions to better manage the overall health and productivity of site operations. This unit provides critical measurements and calculations needed for herd health, ventilation assessments, grain storage management, nutrition strategy development, livestock protection, and more. Easily export and analyze weather information with optional LiNK wireless Bluetooth® technology.

The Kestrel 5500AG Agriculture Weather Meter is a complete tool designed to meet the needs of agriculture production, both livestock and crop. This lightweight, handheld, multi-function meter can be used inside and out for barn/facility environmental assessments, commodity storage, and field and spraying monitoring. With optional wireless data transfer, current and logged data can be easily sent to your mobile device or laptop.

The Kestrel DROP D2AG Livestock Heat Stress Monitor is a small data logger that tracks temperature, humidity and THI in any indoor or outdoor location. Extremely low cost and easily read on your mobile phone from up to 100’ away, you can afford to place many Kestrel DROPs around your facility.

Each of these products were engineered with input from cattle heat stress experts for maximum utility and ease of use: Dr. Daniel Thomson, Kansas State University; Dr. Tom Noffsinger, Production Animal Consultation; Dr. Kev Sullivan, Bell Veterinary Services; Dr. Donald Spiers, University of Missouri.

The Kestrel Cattle Heat Stress trackers were developed for producers to improve summer heat stress and year-round thermal management to maintain herd performance, minimize production losses, protect cows and increase the bottom line.

The kestrel line of Agriculture monitors and meters

"An excellent example of extreme heat and humidity problems is the heat period of July 2006 which resulted in the death of approximately 20,000 animals."
- Heat Stress in Cattle
  Dairy Herd Management

Manage cattle heat stress


Managing heat events and implementing the proper management plans can mean the difference between life and death of your cattle and send savings straight to your bottom line. With accurate microclimate environmental data and cattle-specific heat stress measurements from your Kestrel Cattle Heat Stress Tracker, you will know when and where it is necessary to implement your plan.

There are a variety of management options available depending on the site characteristics and options available to your location. These can include:

  • Providing temporary or permanent shade structures, particularly over vulnerable animals
  • Adding fans or performing fan maintenance
  • Improving air flow by adding baffles
  • Using soakers when THI levels rise
  • Changing the nutrition mix or adjusting feeding schedule
  • Increasing availability of water to ensure all animals have ready access
  • Removing manure buildup, which creates additional heat
  • Changing the cow density

Below is a sampling of links from widely respected organizations with recommendations as to how to manage cattle during an extreme heat event:

Manage Heat Stressed Dairy Cows

"Based on a milk price of $13/cwt, St-Pierre et al. (2003) calculated annual losses of $897 million for the dairy industry in the United States due to heat stress even when current, economically optimal heat abatement systems were used. This loss is almost $100 per dairy cow per year. Without heat abatement systems, the total annual loss would be $1.5 billion, or about $167 per dairy cow per year,"
- Economics of Heat Stress: Implications for Management

Maximize your cattle heard's performance with the Kestrel heat stress tracker


Implementing a measurement-based heat stress management plan helps you maximize herd PERFORMANCE and profits!

  • Cattle that are not heat stressed can increase milk productionIncrease Milk Production
  • Cattle that are not heat stressed can improve weight gainImprove Weight Gain
  • Cattle that are not heat stressed can reduce feed lossReduce Feed Loss
  • Cattle that are not heat stressed can reduce healthcare costsReduce Healthcare Costs
  • Cattle that are not heat stressed can avoid livestock lossAvoid Livestock Loss
Heat Stressed Cow

"Pro-active Heat Stress Management improves productivity $10-$30 per head."
-Dr. Kev Sullivan, Bell Veterinary Services, Australia.